My questions were: Other than knowing I can let my cases grow that much more - is there any other usefull info from knowing the true chamber length? Should I let the cases grow that much or just trim them to published case length?
The useful information is the fact that you know your exact chamber length. .028" isn't bad. I've seen them a lot farther out than that in a factory chamber.
I wouldn't "let them grow" as you will have all different neck lengths. A good plan of attack would be to measure all of your cases and trim them to the length of the shortest one. That way they would all be the same length and you could use that as your trim to length.
What is the length of your shortest case length as compared to your actual chamber dimensions?
Published lengths etc. are related to SAAMI dimensions. If you want to get the most you can out of a factory chamber and round, then get a little anal and make sure they are all the same length. This will help with consistency when it comes to neck tension although, in the end, with a factory setup, you may not be able to shoot the difference but if you feel better then sometimes that's half the battle.;)